Patients with severe systemic lupus, primarily renal or neurologic, will be treated monthly with intravenous cyclophosphamide infusions plus daily oral prednisone. At the end of six months, a decision will be made regarding satisfactory control of disease activity. Patients who are doing well will be randomized to receive either daily oral azathioprine for 30 months or intravenous cyclophosphamide every 3 months for 30 months. Minor flares will be treated with increased prednisone; major flares will be treated by restarting monthly intravenous cyclophosphamide. Patients who flare on azathioprine maintenance therapy will be switched to cyclophosphamide maintenance therapy. A new feature of this protocol will be contraception using implanted progestins ("Norplant") in all suitable female patients of child-bearing age. (In the past we have generally used either Norplant, injectable progestins or oral contraceptives for this purpose).